1. Field
The invention is in the field of explosives of the solid cast primer or booster explosive type as well as explosives in general of small diameter.
2. State of the Art
With the advent of ammonium nitrate and fuel oil mixtures, known as ANFO, into the explosives industry in the early 1950's, and of other lesser or more sensitive explosive mixtures since that time, ways were sought to develop an initiator for these materials in surface and underground blasting. As a result, the cast primer or booster was developed. The cast primer is made from self-explosives such as trinitrotoluene [TNT], cyclotrimethylenetrinitramine [RDX], pentaerythritol tetranitrate [PETN], and mixtures thereof such as Composition B which contains about 60% RDX, 40% TNT, and some wax as a desensitizer. The first cast products were made with a variety of sensitive cores such as PETN or a coiled detonating fuse.
The known and presently used process for making such cast primers or boosters consists of melting the above-mentioned sensitive explosives or combinations thereof, often at temperatures approaching 100 degrees Centigrade or higher, and casting the melted explosive into molds. The greatest hazard posed by the operation is the risk that the temperature control means may fail, and thus, the explosive may reach decomposition temperature and explode. Aside from this grave risk, the process is inherently dangerous in that self-explosives are being handled which are subject to shock detonation even at lower temperatures. Furthermore, in handling the cast products an extremely sensitive dust may be produced which is even more hazardous than the cast primer itself.
There are disadvantages other than the risk of explosion. The materials used are expensive and some are not available from domestic sources. The molds must, of course, be able to withstand the heat of the melted explosive. Nevertheless, such primers are widely used because they have the advantage of being relatively water resistant. Other combinations of primers and boosters based on water gel and or emulsion-based compositions may display only some water resistance or no water resistance at all.
In the past, there have been attempts to formulate sensitive slurry or emulsion type explosive compositions using aqueous solutions of inorganic chlorate and perchlorate salts, i.e., salts of either the chlorate (ClO.sub.3) or perchlorate (ClO.sub.4) ions. These inorganic chlorate and perchlorate slurries and emulsions have serious drawbacks. Their density has to be carefully controlled by using gases (as small bubbles), micro-balloons or similar inert, insensitive, materials that complicate processing and detract from the energy of the primers.
It is an object of the present invention to make a castable primer explosive to maximize borehole pressure (which is a function of both velocity and density) that uses sensitive inorganic chlorate and perchlorate salts, especially the relatively shock-insensitive sodium perchlorate, instead of self-explosives.
It is another object of the invention to make a cast primer or booster at ambient temperatures and thus avoid the hazard of working with explosives at elevated temperatures.